Recent years have witnessed growing interest in distance image sensors that measure distance by the time-of-flight (ToF) method. A distance image sensor may be configured, for example, with a pixel array having multiple SPAD pixels arranged two-dimensionally using complementary metal oxide semiconductor (CMOS) integrated circuit technology. In a SPAD pixel impressed with a voltage far larger than a breakdown voltage, a single photon incident on a high-electrical-field PN junction region triggers avalanche amplification. At that point, the time in which a current flows instantaneously is detected to perform highly accurate distance measurements.
For example, PTL 1 discloses a technology by which a photodiode array made of avalanche photodiodes is structured to provide isolation between pixels so as to reduce crosstalk with adjacent pixels caused by light emissions in high electrical field regions.
Also, PTL 2 discloses a technology by which SPADs embedded with a layer that forms high electrical field regions are depleted with bias to improve the sensitivity of SPAD pixels.